Conventional lead-acid vehicle batteries comprise a number of cells disposed in a container. A series of alternating positive and negative electrodes (plates), having separators sandwiched therebetween, are disposed in each cell and immersed in aqueous sulfuric acid electrolyte. The positive plate contains lead oxide disposed on a lead alloy grid. The negative plate contains lead as the electroactive material on a lead alloy grid.
In lead-acid batteries, gases are often liberated from the electrolyte during the charge and discharge reactions. Factors such as high current charge and discharge conditions, and changes in temperature, can affect the rate at which these gases are produced. To avoid excessive gas pressure buildup which can lead to electrolyte leaks, housing failure, and possibly explosion, it is desirable to vent the high pressure regions within the battery. Due to the volatile nature of these gases, it is desirable to prevent the collection of any substantial amount of these gases.
The vent systems of sealed lead-acid batteries release gases intermittently as the pressure builds up internally during charging or discharging. Hydrogen and oxygen gas tends to accumulate in the space around the vent in the battery vent well external to the battery cell. If enough hydrogen and oxygen gases accumulate, there exists the chance of an explosion due to a spark external to the cell. In some vent constructions, evolved gases pass radially from a central barrel past a one-way relief valve in the form of a flexible band fitted about a hole through the wall of the barrel. See, for example, Gates U.S. Pat. No. 3,862,861, issued Apr. 7, 1987 and Sonnenshein U.S. Pat. No. 3,257,237 issued June, 1966 and U.S. Pat. No. 3,765,942, issued Oct. 16, 1973.
Other patents owned by a common assignee address the problem of preventing battery explosions by providing an explosion attenuating material of closely packed pillows made of a foam or a fibrous material such as polypropylene. See Binder et al. U.S. Pat. No. 4,751,154, issued Jun. 14, 1988, and U.S. Pat. No. 4,859,546, issued Aug. 22, 1989.
An apparatus is needed which reduces the amount of hydrogen and oxygen gases which can collect in the vent cap area so that the danger of explosion from an external flame or spark is reduced. A known device like that shown in FIG. 1 has been used, either with an empty space surrounding the vent barrel, or with a polyester foam filler. Neither arrangement provided explosion attenuation. Polyester, while more useful than no foam at all, burned too readily. Accordingly, a need persists for a battery vent construction wherein the space outside the relief valve between the vent cap and battery cover has an effective explosion attenuation device.